Among known medical needle devices are, for example, indwelling needle devices, which are used for infusion and blood transfusion. A known indwelling needle device is one in which a needle portion projecting from a tip of a cylindrical body has a double structure including a soft outer needle and a hard inner needle (see Patent Documents 1 and 2).
In such an indwelling needle device, when the hard inner needle which has been caused to project from the soft outer needle is inserted into a patient's arm etc., the soft outer needle is also inserted along with the hard inner needle. Thereafter, the hard inner needle is pulled into the cylindrical body, whereby only the soft outer needle is left at the insertion site. As a result, even when the patient moves, pain at the insertion site can be relieved and damage to a blood vessel can be prevented.
The hard inner needle is integrated with the inner hub to which a tube is connected. By pulling the tube, the inner hub is moved, so that the hard inner needle integrated with the inner hub is pulled into the cylindrical body.
In the above indwelling needle device, a drug solution etc. is supplied through the tube to the inner hub connected to the tube and then passed through the soft outer needle before being administered into a patient. When the drug solution etc. is administered, if air is present in the indwelling needle device, the air enters a blood vessel along with the drug solution etc.
Therefore, prior to insertion, the indwelling needle device is filled with a liquid, such as physiological saline, a nutrient solution, etc. This operation is called priming.